Who were Atticus Finch's first two clients?
As Scout is giving an overview of Maycomb in chapter one, she talks about her father establishing his law practice. His first two clients were linked to his first case. Apparently, a blacksmith had detained a mare that was owned by the Haverfords. This means that the blacksmith probably wanted payment for shoeing the horse, but the Haverfords wouldn't pay. Instead, they killed the blacksmith somehow—it doesn't say—and said that he had it coming. Hence, they pleaded not guilty to first-degree murder because they felt that they were in the right for killing the man. The state offered to drop the charge to second-degree murder (with life in prison most likely) if they would just plead guilty. The Haverfords refused the plea deal and Atticus developed a "profound distaste for the practice of criminal law" (5). Therefore, the first two clients Atticus had were the Haverfords and "the last two persons hanged in the Maycomb County jail" (4).
Atticus's first two clients were the Haverford brothers.
When Atticus first opened his practice in Maycomb, he took the case of the Haverford brothers. The two men had killed a local blacksmith when that man had detained their horse. Not only did they kill him, they did so in front of three witnesses and then claimed that since the man had it coming, they shouldn't be in trouble.
Even when they could have escaped a death sentence by accepting a second-degree murder plea, they refused. The Haverfords felt justified in what they'd done and so chose to die rather than accept that they were guilty of murder.
Scout says that her father couldn't do much other than be there for their deaths. She says it's likely what made Atticus dislike practicing criminal law.
The answer to this question can be found in Chapter 1. We do not really know the names of the two clients (we know that their last name is Haverford). But we do know something about them. Scout says that her dad's first two clients were the last two men ever hanged in Maycomb's jail.
These were a couple of idiots who killed a respected man in the presence of witnesses and then were too stupid to take the plea bargain that was offerred to them -- one that would have saved their lives.